Thruster devices are often used in the space industry, particularly for low power applications such as orbital positioning of a spacecraft. In particular, a thruster device, such as a solar thruster, may be used for correcting or maintaining the orbit of a satellite. Another application of thruster devices is to change or alter the orbital path of a satellite in order to avoid detection by other satellites or ground tracking devices.
Conventional solar thruster devices typically comprise a heat exchanger made of a material having a high coefficient of thermal conductivity, such as rhenium, tungsten, or halfnium carbide. The heat exchanger typically includes or defines a flow passage through which a working fluid or propellant is directed such that the solar energy incident upon the heat exchanger is transferred to the propellant. The high temperature propellant is then expelled from the thruster device by expansion through a nozzle, thereby producing thrust. The thrust is used by the satellite to maneuver between orbits or maintain a particular location.
The solar energy used by the thruster is gathered by the heat exchanger by means of a primary concentrator in conjunction with a secondary concentrator. The primary concentrator receives solar energy directly or by reflection and transfers this energy to the secondary concentrator which, in turn, directs the solar energy to the heat exchanger of the thruster device. The energy absorbed by the heat exchanger is then transferred to the propellant within the flow passage. The role of the flow passage is to provide a relatively long flow path along which the propellant can be heated and to direct the propellant to the nozzle. The most effective approach to achieving high thruster performance is to attain a high propellant temperature. The key to achieving this desirable high propellant temperature is dependent on the maximum allowable heat exchanger temperature as well as its thermoconductivity and other properties.
While the use of thruster devices is known, conventional thruster devices can be relatively difficult to manufacture. In particular, a conventional thruster design typically includes a flow passage formed by winding sections of three-foot metallic tubes around a cylindrical mandrel. The cylindrically wound tubes provide a large surface area for transferring solar energy to the propellant. The tubes are typically comprised of a refractory metal capable of withstanding high temperatures, such as rhenium. However, as the tubes are wound around the mandrel, the metal tubes work harden and are very difficult to form to the desired shape. In addition, the tube sections must be welded together prior to winding around the mandrel. Thus, this design requires a tedious, time-consuming and costly fabrication process.
Another conventional thruster device developed by Boeing comprises a cylindrical capsule-like body portion having a nozzle at one end. In contrast to winding a tube around a mandrel to form the flow passage, a series of spirally wound grooves are formed in an inner liner of the body portion, and an outer layer of the body portion is slid over the inner liner to form a spiral channel that directs propellant to the nozzle. This design, however, requires that the diameteral clearance between the inner and outer liners be closely matched to avoid chafing between the liners upon assembly. In particular, chafing can damage the seal between the grooves forming the channel, which can have a deleterious effect on the flow of propellant and result in a loss of thrust.
In yet another design, a rhenium foam is positioned between two rhenium sheets to form a flow passage. However, this thruster design has not been proven experimentally.
Thus, there is a need for a thruster device that offers the same or improved performance relative to conventional thruster devices with reduced fabrication costs. In particular, it would be desirable to fabricate the thruster device without having to wind tubes around a mandrel to form the flow passage. There is also a need for providing a thruster device that can be easily assembled without damaging the flow passage.